NOVEL METHOD OF PREPARING SECONDARY BATTERY

A method of preparing a secondary battery including pre-lithiating an electrode assembly including an electrode structure including a plurality of electrodes and a plurality of separators, and a metal substrate. The plurality of electrodes and the plurality of separators are alternatingly stacked. The pre-lithiating includes supplying lithium ions from one of the plurality of positive electrodes to one of the plurality of negative electrodes up to a state of charge (SOC) of A % by electrically connecting one of the plurality of positive electrodes and one of the plurality of negative electrodes and applying a first current, supplying lithium ions from the metal substrate to the positive electrodes up to B % of capacity of the positive electrodes by electrically connecting the metal substrate and the positive electrodes and applying a second current, after applying the first current, and resting the electrode assembly, after applying the second current.